I think the wording about "business need" is really about exceptional circumstances, not a day-in-day-out expectation of extra hours because of 'culture'. That's not some gotcha clause to get you to work regular extra hours for no extra pay.
I think of myself as self-employed, just on a long-term contract. My customer wants exclusivity, 35 hours a week of work from me, fulfilled between 8-6 monday-friday. They agreed to pay me a certain salary in return for my labour and expertise as well as few other things like pension, sick pay, private medical insurance and so on. If they asked me to work additional hours I would either decline or negotiate additional fees. If I asked for more money because of my specific short term needs, they would likely decline.
If there was a special event, or piece of work that needed additional working hours, well if it was known about in advance I'd ask for more money. If it were a surprise, well as long as it fitted in with me I would try to be flexible and help out the business. But I'd expect the same in return if I needed to pick up a relative from hospital, or wanted an extra half an hour on my lunch break. Bit like in the Godfather. I'll do this for you, but the unspoken undertone here is that the employer owes you a favour now.
If employee-employer relationships are only one way, they are abusive. Employers have gotten away with 'its the culture here' stuff for too long. Often its on the promise of progression that never materialises and stems from a desire to squeeze the workers until the pips squeak then either rake in the profits of free labour or boast to the next level up boss about their "productivity."
If you a partner or major shareholder, or commission earner, crack on, but that is an individuals choice.
Don't be a martyr. Do your hours. If standing up to management doesn't get you anywhere, other posters have good suggestions re: HR etc. By all means be flexible if an unusual circumstance arises, but only if that is reciprocated. Remember, we advise people on here in abusive relationships to LTB.